Development of the Remarkable Pollen Apertures of the Jellyfish TreeMedusagyne oppositifolia(Ochnaceae, Malpighiales)

Abstract

Pollen development is examined in Medusagyne oppositifolia, a critically endangered tree endemic to the Seychelles. Formerly placed in its own family, M. oppositifolia is now assigned to Ochnaceae in Malpighiales. Pollen and tapetal characters have previously been shown to be of systematic importance in Malpighiales. The pollen of M. oppositifolia has remarkable projecting porate apertures, but their development was previously unknown. Pollen development was studied using transmission electron microscopy (TEM) of sections of anthers obtained from buds of cultivated M. oppositifolia. Amorphous endexine is deposited without the involvement of lamellae, a rare form of endexine deposition in flowering plants. This flexible endexine is pushed into position inside the atria (apertural cavities) by the expanding intine. Foot layer, not endexine, is deposited on lamellations with white lines, which is highly unusual. Extremely large onci, consisting of fibrillar spacer material, begin development during the tetrad stage and are located between the extexine and developing endexine in immature microspores, forming the atria. The secretory tapetum produces many orbicules (sporopollenin bodies). Pollen development in M. oppositifolia shows some highly unusual features. Despite this, it does share some characters with other Malpighiales. Similar endexine occurs in Passiflora (Passifloraceae) and similar orbicules in Populus (Salicaceae). A lamellated foot layer may also occur in Ochna (Ochnaceae), though this requires further study.